In certain applications, it is desired to use energy from a direct current (DC) source with devices and/or systems that are configured to utilize alternating current (AC) energy. In such applications, an inverter may be used. Inverters are used to convert a direct current supplied by a source to alternating current for use by devices and/or systems.
Examples of such applications may be found in vehicle systems. For example, rail vehicle systems may include one or more powered units (such as locomotives) used to transport one or more non-powered units, such as passenger and/or freight cars. The non-powered units may require AC power for correct operation. Such power may be provided, for example, from a powered unit to one or more non-powered units in a head end power (“HEP”) arrangement. For example, if the non-powered units are used as passenger cars, then power may be required for heating or cooling a passenger car, providing lighting for the passenger car, or outlet power for other passenger necessities or conveniences. Similarly, if the non-powered units are used as cargo cars, such cars may also require power for lighting, refrigeration, or other uses. Such power may be provided from a powered unit through an HEP system.
The powered units of such a vehicle system typically utilize a direct current energy source, such as a battery and/or generator that is charged or powered by a prime mover, such as a diesel engine. However, the non-powered units, and/or portions of the powered unit, may be configured to utilize alternating current. Thus, one or more inverters may be used to convert the power from the direct current source to alternating current for use in non-powered cars or those portions of powered units that utilize alternating current.
Some known inverters, however, suffer from certain practical drawbacks. As one example, the amount of power required for certain HEP applications may exceed the capacity or capabilities of practical and/or available inverters. In such circumstances, more than one inverter may be used. However, the alternating current output of the inverters may then differ, for example, in period and/or in the timing of certain events in their output wave, such as upper or lower peaks. The resulting unsynchronized or mismatched outputs can then result in reduced efficiency and/or performance caused for example by interference, noise, and/or various output waves cancelling each other out.
A need exists for improved performance in systems having multiple inverters.